It has been conventional practice for many years to use thermocouples attached to the sidewalls of glass fiber forming bushings. Such bushings are electrically heated and are coupled to power transformers for supply of electrical current thereto. The power level supplied to the resistance heated bushings is controlled by a controller unit. The output signal from the sidewall thermocouple is fed into the controller unit. The controller measures the signal, compares it against a reference and then makes necessary changes in the power supply to the bushing.
In practice, it has been found that such sidewall thermocouples are less accurate than desired in determining the representative temperature of the glass material inside the bushing at the orifice section of the base plate. Also, the reaction time of such sidewall thermocouples in sensing changes in the temperature of the glass material at the orifice section of the base plate is slower than desired. Thus, improved method and apparatus for sensing and controlling the temperature of the glass material inside a glass fiber forming bushing at the orifice section of the bottom wall is desired.